The invention relates to a device for drilling a bore in the ground.
A device of this type is disclosed by WO 97/34070. The percussive tools are in this case connected directly in a plurality to the tool head, so the percussive energy is transferred via the drive medium to the tools sunk in the bore and from said tools directly to the base of the bore, so that the connecting rod assembly remains largely unaffected thereby. The tool head is connected via the connecting rod assembly to a drive device, normally arranged outside the bore and having a rotary drive, so that the tools arranged on the tool head operate at points on the base of the bore which are always new. The devices mentioned are mostly used to operate in solid rock.
In practice, this type of drilling is of increasing importance since, firstly, the quality of the bores is better and the direction of the bores can be maintained virtually exactly; secondly, because of the sound-absorbing method of use in the bore without any substantial external effect, environmental criteria such as noise nuisance are satisfied considerably better.
In installations of this type, transporting the rock material separated and excavated away at the face or the base of the bore out of the bore can be carried out within the hollow connecting rod assembly in the manner of what is known as “reverse circulation”. For instance, the air lift method can be used for this purpose, in which air as a flushing medium is blown into the drilling assembly above the tool head, so that the air rising in the connecting rod assembly produces a pressure difference in the connecting rod assembly between bore and surface, which induces a flow velocity in the connecting rod assembly, with which the rock material is driven out through the connecting rod assembly.
In the case of the known device, percussive hammers are used as tools. Although, by using this device, satisfactory drilling progress is achieved, in particular in hard rock, it is disadvantageous that the drilling efficiency decreases, in particular in softer strata.